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SCAAC in Vitro Derived Gametes June 2020.Pdf Strategic delivery: ☒Safe, ethical, ☐Consistent outcomes ☐Improving standards effective treatment and support through intelligence Details: Meeting Scientific and Clinical Advances Advisory Committee (SCAAC) Agenda item 6 Paper number SCAAC (08/06/2020) 006 Meeting date 08 June 2020 Author Victoria Askew, Policy Manager Output: For information or For information recommendation? Recommendation Members are asked to: • consider the progress in research (since October 2016) into in vitro derived gametes; and • advise the executive if they are aware of any other recent developments; and • review whether any outputs from the HFEA are required addressing the use of in vitro derived gametes. Resource implications N/A Implementation date N/A Communication(s) N/A Organisational risk ☒ Low ☐ Medium ☐ High Annexes None Human eggs and sperm (germ cells) are derived from a type of cell called primordial germ cells (PGCs). They are produced in the ovaries of a woman or testes of a man by a process called gametogenesis. Researchers are investigating whether it is possible to carry out gametogenesis in the laboratory using PGCs, embryonic stem cells (ESCs) or other human cells. Eggs and sperm derived from such cells in the laboratory are called in vitro derived gametes. The legislation in the UK (the Human Fertilisation and Embryology Act 1990, as amended) prohibits the use of in vitro derived gametes in treatment. Section 3ZA requires that eggs or sperm permitted for treatment are “produced by or extracted from the ovaries of a woman/testes of a man”. Whilst in vitro derived gametes cannot be used in treatment in the UK, they can be used in research, for example, research into germ cell development and cell differentiation. Researchers in the UK need an HFEA research licence if they wish to investigate whether human eggs and sperm derived in vitro could undergo fertilisation and the early stages of embryo development. It is therefore important that the HFEA is aware of the progress of research in this area. The committee last reviewed research on in vitro derived gametes in October 2016. The committee discussed the need for transplanting in vitro derived gametes back into the ovary or testes in the later stages of maturation to allow imprinting to occur, and that ideally when culturing in vitro derived gametes the supporting somatic cells would also be derived in vitro. The committee also questioned to what extent mouse models are an accurate model for human development. An expert external speaker attended the October 2016 SCAAC meeting and informed the committee that progress in research in 2016 had been able to derive gametes without implantation back into ovaries or testes, however stated that these results needed to be reproduced. The speaker explained to the committee that there are differences in regulation of the pluripotent network between mice and humans, as well as differences between germ cell transcriptome and post-implantation development. However, animal models are required in the UK and pigs can be an affordable and accessible model for human development. The speaker acknowledges that a robust methodology for deriving germ cells from somatic cells was yet to be developed and that successful derivation of high-quality cells in humans would still be a number of years away. At the February 2020 SCAAC meeting one Committee member commented that the pace of research for in vitro derived gametes is not as fast as in other topics such as genome editing, and milestones are happening slowly, but the committee still need to be aware of developments. This review highlights key developments in animal and human studies with a focus on developments since October 2016. A study conducted by Zhou et al. (2016) reported complete in vitro meiosis from ESC-derived primordial germ cell like cells (PGCLCs). Co-culture of PGCLCs with neonatal testicular somatic cells and sequential exposure to morphogens and sex hormones reproduced key hallmarks of meiosis, including erasure of genetic imprinting, chromosomal synapsis and recombination, and correct nuclear DNA and chromosomal content in the resulting haploid cells. Intracytoplasmic injection (ICSI) of the resulting spermatid-like cells into oocytes produced viable and fertile offspring, showing that this stepwise approach could functionally recapitulate male gametogenesis in vitro. Hikabe et al. (2016) reported the first successful reconstitution in vitro of the entire process of oogenesis from mouse pluripotent stem cells. Fully potent mature oocytes were generated in culture from ESC and induced pluripotent stem cells derived from both embryonic fibroblasts and adult tail tip fibroblasts. Pluripotent stem cell lines were then re-derived from the eggs that were generated in vitro, thereby reconstituting the full female germline cycle in a dish. In 2016, Ishikura et al. found that when aggregated with reconstituted testes in vitro, PGCLCs induced from mouse ESCs differentiate into spermatogonia-like cells in vitro and were expandable as cells that resemble germline stem cells (GSCs). The findings showed the GSC-like cells (GSCLCs), but not PGCLCs, colonised adult testes and contribute to spermatogenesis and fertile offspring. Compared to GSCs derived from neonatal testes, GSCLCs exhibited a limited capacity for spermatogenesis. Whole-genome analyses revealed that the GSCLCs exhibited aberrant methylation at vulnerable regulatory elements, including those critical for spermatogenesis, which may restrain their spermatogenic potential. Oblette et al. (2017) undertook the first study assessing the differences in nuclear quality between fresh and frozen/thawed (using either controlled slow freezing (CSF) or solid surface vitrification (SSV)) mouse spermatozoa cultured in vitro with in vivo controls. No significant difference was found in rate of aneuploidy, DNA fragmentation or chromatin condensation between either the fresh or frozen/thawed in vitro cultured spermatozoa and in vivo controls. However, the yield of spermatozoa from in vitro culture is lower than that in vivo. The culture conditions will need to be further optimised to allow greater yields for the analysis of epigenetic modifications, embryonic development and spermatozoa at the ultrastructural level by transmission electron microscopy. A study by Dumont et al. in 2017 investigated the effects of cryopreservation and in vitro culture on the expression of proteins involved in apoptotic or autophagic pathways in the pre-pubertal testicular tissue of mice. The impact of cryopreservation procedures was minimal at the end of the culture. However, in vitro culture modified apoptosis- and autophagy-related relative protein levels compared to in vivo controls. The authors argue that a disturbance in the balance between pro- and anti- apoptotic proteins expression during in vitro culture could be one of the reasons for altered apoptosis in less effective (or impaired) spermatogenesis. Rondanino et al. (2017) used immature fresh and frozen/thawed testicular tissue of mice to analyse whether an intact blood–testis barrier (BTB), which is essential for the progression of spermatogenesis, could be replicated in in vitro culture. In vitro culture exhibited the correct expression and localisation of major BTB components (CLDN11, CX43 and ZO-1), Sertoli cell maturation, as well as the progression of spermatogenesis at the same pace as in vivo. However, CLDN3 expression was decreased and meiotic and post-meiotic progression was altered in cultured testicular tissues. There was an increased BTB permeability and a decreased expression of the androgen receptor regulated gene Rhox5 at the end of the culture period in comparison with in vivo controls. The completion of in vitro spermatogenesis occurred in seminiferous tubules with an intact BTB, both expressing and lacking CLDN3. Investigations by Ohta et al. (2017) showed that the combined application of Forskolin and Rolipram, which stimulate cyclic adenosine monophosphate (cAMP) signalling via different mechanisms, expands PGCLCs up to around 50-fold in culture. The expanded PGCLCs maintain robust capacity for spermatogenesis. During expansion, PGCLCs comprehensively erased their DNA methylome, including parental imprints, in a manner that precisely recapitulated genome-wide DNA demethylation in gonadal germ cells, while essentially maintaining their identity as sexually uncommitted PGCs, apparently through appropriate histone modifications. By establishing a paradigm for PGCLC expansion, the system reconstituted the epigenetic "blank slate" of the germ line, an immediate precursory state for sexually dimorphic differentiation. A recent review by Maker et al. (2019) considered publications investigating the mechanisms leading to germ cell development in mammals, particularly in mice and non-human primates, as well as the applicability of these animal models to human germ cell development. Mouse models have provided essential mechanistic insight into the process of germ cell lineage development. However, there are several structural differences between mice and humans during early embryogenesis that hinder the extrapolation of findings made in murine models to what may occur in humans. Recent studies using human or non-human primate embryos and human-induced pluripotent stem cell (hiPSC)- derived germ cells shed light on key cellular and genetic mechanisms governing germ cell development in humans. Utilising the knowledge obtained from studying germ cell development in different animal models, induction
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